Electrostatic deflector for selectively and adjustably bending a charged particle beam

ABSTRACT

An electrostatic deflector consisting of a central plate and a pair of outer plates spaced from and parallel to each other. Each plate is provided with a slot for line of sight passage through the deflector and the central plate is charged at a high constant voltage with respect to the outer plate.

United States Patent- [72] Inventors James D. Larson [50] Field ofSearch 250/495 Upton; (0),49.5(3),49.5(9).4l.9(3),4l 9(lSE); 'John A.Benjamin,Stony Brook, N.Y. 313/78, 80; 313/78, 80 [2| l App]. No.712,568 221 Filed Mar. 12, 1968 1 References Cited [45] Patented Jan.26, 197] UNlTED STATES PATENTS 1 Assignee the United States of Americaas represented 2,5 80,675 1/1952 Grivet et al 250/495 by the UnitedStates Atomic Energy Commission FOREIGN PATENTS 1,352,167 1/1964 France25Q/49.5

[54] ELECTROSTATIC DEFLECTOR FOR SELECTIVELY AND ADJUSTABLY BENDING ACHARGED PARTICLE BEAM 1 Claim, 2 Drawing Figs.

[52 US. Cl 250/495, 250/419; 313/80 [5 1] Int. Cl HOlj 37/00, H01 j39/34 HIGH VOLTAGE D.C. SUPPLY Primary ExaminerWilliam F. LindquistAttorney-Roland A. Anderson ABSTRACT: An electrostatic deflectorconsisting of a central plate and a pair of outer plates spaced from andparallel to each other. Each plate is provided with a slot for line ofsight passage through the deflector and the central plate is charged ata high constant voltage with respect to the outer plate.

ION BEAM PATENTEDJAHZSIQYI 3558379 BEAM SOURCE z BEAM SOURCE ISPECTROMETER ION BEAM HIGH V-OLTAGE 0.c. SUPPLY INVENTOR.

JAMES B. LARSON BY JOHN A.BENJAM|N BACKGROUND OF THE INVENTION.

electrostatic device is alsocapable of fast switching as very littleenergy is stored. and furthermore such a device is able to deflect ionsof different masses of thesame energywithout separating them.

One of the principle drawbacks and limiting factors in- .volved in theuse of; electrostatic deflectors is that such devices usually employ ascreen or grid. through which the beam passes to effect its deflection.The presence of the grid tends to attenuate the beam and its presence inthe electric field has a tendency to produce small lenslike regionswhich defocus the beam by acting on separate portions of the beam. Inaddition, the grid eventually burns out as a result of sputtering andproduces secondary emissions of electrons when struck by the ion beam.-

SUMMARY OF Tl-IE INVENTION The invention described herein was made inthe course of, or under a contract with the US. Atomic EnergyCommission.

The present invention overcomes or reduces the disadvantages anddrawbacks of presently used electrostatic deflectors by avoiding the useof a screen through which the beam passes. In accordance with thisinvention, three spaced electrodes arearranged with aligned slots. thecentral electrode being charged at a different voltage than the outsideelectrodes. In a typical application of this device. the electrodes aremounted at a 45 angle with respect to the path of the ion beam whichpasses through the slots without contacting any of BRIEF DESCRIPTION OFTHE DRAWING I FIG. 1 shows schematically a typical application of thisinvention;

FIG. '2 shows an isometric view. in partial section, of a preferredembodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there isillustrated a mass spectrometer M arranged to receivean ion beam fromeither of ion sources 51 and S2. The former is located with respect tospectrometer M in such a way that its ion beam will pass directly intospectrometer'M. The latter is located at a position offset from theentrance to spectrometer M, as shown, Electrostatic deflector 1:0 madein accordance with this invention, is placed in line.

with both the entrance to spectrometer M and the beam produced by sourceS2. When only source 81 is generating a beam. the beam fromsource S1will pass through deflector without any interference or attenuation, aswill be seen later. When 51 is not generating and S2 is producing abeam. deflector 10 is energized and the beam from S2 is reflected intospectrometer M. While this deflection, angle A. is a right angle in theillustration. it is understood that other angles are possible.

For the details of deflector [0. reference is made to FIG. 2 where it isseen that it. consists of electrodes which are spaced flat plates 12. l4 and 16 parallel to each other. Plates. [2. l4.

and I6 whichare made fromelectrically conductive material 24 must belarge enough to accommodate in a similiar fashion to the size of thebeam to be accommodated.

Center plate 1,4 is placed at some DC voltage with respect to outerplates l2 and 16 from a DC power supply E. the polarity of course beingthe same as the charge on the ions to he deflected. While outer plates12 and 16 are shown as being grounded (i.e. same potential). therelative voltages may be varied without departing from the principles ofthis invention. depending on the characteristics to be imparted todeflector 10. It is seen that the spacing of each of plates 12 and I6.respectively, from central plate 14. as well as the potential dilfcrences existing from central plate 14 to outer plates l2 and 16.respectively, determine the magnitudes and the gradients of the electricfields existing in the separating spaces. Thus. if deflector 10 issymmetrical both geometrically and electrically. and the charge on theplates is insufficient to deflect beam away as shown in FIG. 2. a beamof properly charged ions passing through deflector 10 will not be bentin its direction, but will be offset laterally. somewhat similar to theeffect a glass plate has on a beam of light striking it at an angle. dueto differences in the index of refraction.

In the event that the intensity of the electric fields is suffrcient toprevent the beam from passing through deflector I0, the angle ofreflection C is alwaysequal to the angle of in cidence B, shown inFIG. 1. 7

An electrostatic deflector incorporating the principles of thisinvention has been found useful to bend both positive and negative ionbeams, including H- and H+ ions, and heavier ions including those ofoxygen. Oneof the particular advantages of this invention when used inbending beams of heavier ions is that the deflector itself does not haveto be increased in mass as is the case when magnetic devices areutilizecl. In addition, because the deflector does not store significantamounts of energy, it can be switched on and off with far greaterrapidity than a magnetic deflector is capable of because of theexpanding and collapsing magnetic field phenomenon.

Another important advantage of the inventive arrangement arises from thefact that the deflector tends to focus the beam in a plane withoutdefocusing in a transverse plane. Thus more than one of these devicescan be utilized to control independently the focal properties of beams.

It is thus seen that there has been provided an improved electrostaticdevice of which while only a preferred embodimerit of the invention hasbeen described, it being understood that many variations thereof arepossible without departing from the principles of this invention asdefined in the appended claims.

Iclaim:

I. An electrostatic deflector for a beam of charged particlescomprising:

a. means placed in line with said. beam comprising three I mountedelectrodes of electrically. conducting material spaced from each other;1

b. said electrodes each having formed therein an opening. the Openingsbeing aligned for unobstructed passage of said beam, said openings beingelongated slots of sufficient lengths to accommodate bending of saidbeam at a right angle without interference by said electrodes; and

c. means for I 3. selectively connecting and disconnecting saidpotential applied to said center electrode to selectively deflect saidbeam or permit the unobstructed passage of said beam through saidopenings.

1. An electrostatic deflector for a beam of charged particlescomprising: a. means placed in line with said beam comprising threemounted electrodes of electrically conducting material spaced from eachother; b. said electrodes each having formed therein an opening, theopenings being aligned for unobstructed passage of said beam, saidopenings being elongated slots of sufficient lengths to accommodatebending of said beam at a right angle without interference by saidelectrodes; and c. means for
 1. maintaining the center electrode at agreater absolute constant voltage potential than the outer electrodes ata polarity to repel said charged particles, the outer electrodes beingat the same potential;
 2. varying said potential to correspondingly varythe angle at which said beam is deflected; and
 3. selectively connectingand disconnecting said potential applied to said center electrode toselectively deflect said beam or permit the unobstructed passage of saidbeam through said openings.
 2. varying said potential to correspondinglyvary the angle at which said beam is deflected; and
 3. selectivelyconnecting and disconnecting said potential applied to said centerelectrode to selectively deflect said beam or permit the unobstructedpassage of said beam through said openings.